Rubio didn't once mention immigration reform during his speech, focusing instead on themes of limited government and criticism of Obama's policies, most prominently his healthcare law.

But his position as one of the chief architects of the immigration reform measure that passed the Senate earlier this year has drawn fierce criticism from conservatives, some of whom say he has sold out since getting elected to the Senate with Tea Party support.

Of particular concern to conservatives is the portion of the law that would create a pathway to citizenship for illegal immigrants currently living in the U.S., as well as what some conservatives believe to be too-lax border security provisions.

Republicans in the House have said the Senate version of the bill is a non-starter.

Since taking a prominent role in the immigration reform debate, Rubio has sought to pivot back to the right to shore up some of the support among conservatives that eroded during that fight.

He's one of a handful of conservative senators leading the push to defund ObamaCare, and on Friday pledged to oppose any budget that provides funding for the law.

“I will not vote for any short-term budget that spends one single cent on ObamaCare,” Rubio said to cheers, according to Reuters. “I will not vote to raise the debt limit unless it comes with a balanced budget amendment.”